Many foods are commercially processed by dipping in a batter and breading followed by cooking in a hot oil bath at suitable temperatures of, say, 360.degree. F. to 380.degree. F. Foods thus prepared are consumed on site or packaged, as by freezing, for distribution.
During use, the oil becomes contaminated by particulates derived from the food, batter and breading as well as by soluble free fatty acids and color bodies. Free fatty acids are continuously produced by breakdown of organic particulates in the hot oil. Since the oil remains hot, particulates allowed to remain therein continue to pyrolize and/or oxidize thus continue the build up of free fatty acids, off-tastes and undesirable color. Free fatty acids as noxious fumes also cause burning of eyes of persons in the frying area.
All of the above problems can be solved, to a degree, by frequent dumping and total or partial replacement of the oil, however, that is very costly because the used oil can be sold only for salvage value for other uses. New oil, besides being expensive, must be reheated which increases its cost. Moreover, even with frequent replacement, the cooker conditions are not constant, but continuously worsen from the time new oil is added until it is dumped.
In prior operation, particulates are removed by screening and crude filtration. This is costly because screening is slow and the resulting solids waste has associated with it much oil that is simply lost. Furthermore, not all particulates are removed, consequently the build up of finer particulates continues with resultant degradation of oil until it must be dumped. In some prior operations, coarse solids are removed by screening or decantation then the resulting partially cleaned oil is subjected to pressure filtration. Again, this is a slow batch type operation.
In accordance with prior practice, removal of free fatty acids is accomplished by mixing the oil with a suitable adsorbent long enough to effect acid removal. This usually requires considerable time, from as low as 20 minutes to an hour or more, during which the oil cools and is out of use. This adds to tankage and oil inventory requirements. It also causes the consumption of extra energy for reheating.
Color removal is effected, independently of free fatty acid control, by suitable treatment of the oil.
From the foregoing it is apparent that significant savings in labor and material will be realized if the cooker oil can be continuously maintained at a constant condition of clarity and acceptable free fatty acid content without unnecessary cooling or loss of significant quantities of oil in waste particulates.